The field of the invention relates to etching apertures in monocrystaline substrates such as silicon.
It is known to etch apertures in silicon substrates by etchant processes commonly referred to as micro-machining. These apertures have been used in optics and also as fluid flow nozzles. Examples of these apertures are enumerated below.
U.S. Pat. No. 4,269,653, issued to Wada et al discloses an aperture etched through silicon for use as an electron beam exposure device. The resulting aperture axis is perpendicular to the nominal plane of the silicon substrate.
U.S. Pat. Nos. 4,628,576 and 4,647,013, both issued to Giachino et al, disclose apertures etched through silicon for use as the nozzle portion of a fuel injector valve. Again, the aperture axis is perpendicular to the nominal plane of the substrate through which the aperture is etched.
IBM Technical Disclosure Bulletin, Volume 14, No. 2, July 1971, Pages 417-418, entitled "Fabricating Shaped Grid and Aperture Holes", discloses a method for etching an array of apertures for use as illumination apertures. More specifically, a silicon substrate is shown having an epitaxial layer grown thereon. A desired array or pattern of apertures is etched through the epitaxial layer. An etchant which attacks the silicon substrate, but not the epitaxial layer, is then used to etch the substrate off from the backside thereby exposing the epitaxial layer and the pattern of apertures etched therethrough. Each aperture has an aperture axis perpendicular to the epitaxial layer.
U.S. Pat. No. 4,169,008 discloses a method of etching apertures for use as nozzles in ink-jet printers. Etchant pits in both the top and bottom surfaces form an opening having an aperture axis perpendicular to the nominal plane of the wafer. By etching from the bottom side, it it alleged that variations in the aperture openings are avoided which would otherwise occur due to variations in the wafer thickness. Stated another way, the dimensions of the openings in the bottom planar surface are determined by the bottom mask openings, rather than by the intersection of the top etchant pit with the bottom planar surface. Each aperture axis is perpendicular to the nominal plane of the substrate.
A problem with the above approaches is that the angle of the aperture plane is not selectable. The aperture axis is constrained to a direction perpendicular to the nominal plane of the substrate. Additional structure is needed to direct the fluid flow in a direction other than perpendicular to the substrate plane which may be desired for a particular application.